What's Your Ideal Weight?

Dropping five pounds will make you healthier and faster--as long as you have them to lose

Some runners don't worry much about their weight. they think: I run, therefore I can eat a cow for dinner. However, these same runners will gain 3.3 pounds per decade, according to a recent analysis of 4,700 midlife male runners from the National Runners' Health Study. That's not a lot, but it does add up, and the gain strikes even those running more than 40 miles a week. The same runners also gained three-quarters of an inch around the waist every decade–goodbye six-pack abs!

I've always monitored my body weight closely, believing I have an American birthright to obsess over it, just like Oprah, Jared, and millions of others. I also figure there are two solid reasons to get on the scale every Saturday morning: I want to find and maintain my healthiest weight, and I also want to determine my fastest weight. I suspect I'm not the only runner who's interested in these two.

Twenty years ago, when reading some early studies on body mass index (BMI) and longevity, I cringed. People of my BMI–I'm relatively tall and skinny, with a BMI around 21.0–were dying younger than others a little heavier than I. (You can quickly determine your own BMI using the tool in the Nutrition & Weight Loss channel on runnersworld.com.)

On a recent visit to California, I visited Bill Haskell, Ph.D., to ask him about the weight and longevity question. He's the director of Stanford University's Prevention Research Center and a guy who's been at the epicenter of important health-fitness debates for 30 years. "Those first studies failed to eliminate some people who were thin because they smoked cigarettes or were already diseased," Haskell told me. "The newer studies show no increase in mortality until BMI falls into the mid-eighteens."

The National Institutes of Health gives us four marks on the BMI ladder. It puts the underweight/unhealthy BMI cutoff at 18.5, which indicates malnourishment. If your BMI is 18.5 to 24.9, you're in the normal/healthy weight range. From 25.0 to 29.9, you're overweight, and your health risks (such as diabetes, high blood pressure, and heart disease) start climbing. Anyone above a 30.0 BMI gets labeled obese and faces dramatically higher health risks. Approximately 60 percent of all Americans are overweight or obese, and this percentage is increasing.

Fat and Fit?

While it seems certain that higher body weights are unhealthy, fitness counts, too. Steven Blair, P.E.D., who often describes himself as "short, fat, and bald," is the most famous expert in the BMI, exercise, and health field. He and his former colleagues at the Cooper Aerobics Center have collected the world's most impeccable fitness data; they've actually tested thousands of subjects on a treadmill. Most other large studies are based on questionnaires that ask: "How much do you exercise during a typical week?" And you just know a lot of people are wildly optimistic (lying) when they answer that question.

The Cooper Center studies show that aerobic fitness is a powerful predictor of longevity. Indeed it's often better to be fat but fit rather than lean and out-of-shape. Fitness can trump fatness. As a result, Blair, a lifelong runner now at the University of South Carolina, believes we focus too much on weight, which demonizes and demoralizes fat people. "I'd like to banish the whole idea of ideal weight," he says. "We simply don't have enough data to say what's right for any individual or group. We should focus more on telling people they can get healthier by becoming more active, no matter what their starting weight."

That's a great message, and one we should all take to our nonexercising, overweight friends. They need every bit of motivation they can get. Still, we should also remember that weight loss is almost always good. Because lean and fit will always trump fat and fit.

Fast Losers

Of course, some runners are more interested in fastness than fitness. They want to know: What's my best weight for fast 5-Ks and marathons? Will losing weight help? The answer is almost always yes. But, as with BMI, only to a point. Lose too much weight, and you become weaker and slower, not stronger and faster. Many parents and high school and college coaches worry about anorexia nervosa, a psychiatric disease found mostly among adolescent and college-age female runners, dancers, gymnasts, and skaters. The most recent studies show that anorexia affects about .6 percent of the overall population, but four to six times as many young athletes. Since some anorexics actually starve themselves to death, concern is justified.

Still, there's no denying that healthy runners will race about two seconds per mile faster for every pound they lose. Weight loss boosts maximal aerobic capacity (VO2 max), an essential contributor to distance-running potential, because the less weight you carry around, the more miles per gallon you get from your oxygen. And because losing a few pounds makes running easier, you should be able to increase your workout distance and speed. So losing weight helps you train harder.

Recently, a University of Dayton (Ohio) runner and physiologist named Paul Vanderburgh, Ed.D., has focused more academic attention on the subject. A couple of years ago, Vanderburgh, who recently ran a 3:31 marathon at 170 pounds, decided to devise a calculator that would "equalize" performances among runners of different weights. When he had finished his research, Vanderburgh validated his calculator at several Ohio road races, where it performed well. He published his study in the Journal of Exercise Physiology and put his calculator, which he calls the "Flyer Handicap Calculator," on the Internet. You can get there from snipurl.com/agesexweightcalc. Since the calculator also includes age and gender factors, it can be used to compare, say, a 25-year-old woman who weighs 120 pounds with her 55-year-old father who weighs 165. Fun stuff.

"I hope the Flyer Handicap Calculator will level the playing field a little, and give more motivation to heavier runners," Vanderburgh says. For those who simply want to lose weight to get faster, he has this advice: Lose fat, not muscle. Fortunately for runners, many studies have shown that exercise-based weight-loss programs help you achieve this goal much better than diet-only plans. "If you're not already doing some strength training, you might want to begin, since strength training is a great way to retain muscle," says Vanderburgh.

I've never had much luck with strength training, but maybe it's time to try again. I've lost about five pounds this year, on top of 10 the previous several years, by eating less pasta and rice and more fruit, vegetables, and fiber, and drinking water instead of fruit juice. I'm still heavier than my college weight, but I've narrowed the gap to seven or eight pounds. Result: My BMI is still above 18.5, my race times are dropping, and best of all, I feel great.

Lose Weight, Gain Speed

This table, based on changes in maximal aerobic capacity, provides a rough estimate of how much your race times will improve if you lose weight, as long as you have it to lose. If your BMI drops below 18.5, you're at risk of becoming weaker and slower.